1. Field of the Invention
This invention relates generally to automotive windshield wiper systems and, more particularly, to a crank arm assembly between a wiper drive motor and a transmission link of the windshield wiper system.
2. Description of the Prior Art
Typical automotive windshield wiper systems include a drive link connected to the wiper arms and extending across the vehicle, an electric motor, and a crank arm attached to the armature shaft of the motor and to one end of the drive link. When the motor shaft rotates, the drive link reciprocates in strokes determined primarily by the length of the crank arm which reciprocation causes the wiper arms to angularly oscillate between the inner and outer limits of their normal wiping arcs. In depressed park systems, the wiper arms are driven to stowed or parked positions below the inner limits of their normal wiping arcs at the end of the final wiping stroke. In so called reverse-to-park depressed systems, the extra angular movement of the wiper arms beyond their inner wipe limits is the result mechanism in the wiper drive system which automatically increases the effective length of the crank arm in response to the onset of reverse rotation of the wiper motor shaft. In one such system, an eccentric bushing is arranged between the outboard end of the crank arm and the corresponding end of the drive link. The bushing maintains a folded position when the motor shaft rotates in one direction corresponding to normal wiping of the windshield and automatically pivots to an unfolded position when the direction of motor shaft rotation reverses. In another reverse-to-park system, a fixed length crank arm on the motor shaft carries a crank pin which rotates in a fixed orbit around the motor shaft. An intermediate link has one end pivotally connected to the crank pin and the other end pivotally connected to the windshield wiper drive link. A control member is freely rotatable in one direction about the motor shaft axis but is prevented from rotating in the opposite direction by a one-way bearing. The control member defines a guide for the end of the intermediate link where the latter is attached to the drive link. When the motor shaft rotates in the direction corresponding to normal windshield wiping, the crank arm engages a stop on the control member and the latter rotates as a unit with the crank arm in a folded configuration of the assembly. At the onset of motor shaft rotation in the opposite direction, the one-way bearing prevents corresponding rotation of the control member so that the succeeding increments of angular movement of the crank arm relative to the control member effect linear outward displacement of the end of the intermediate link where the latter is attached to the drive link which linear movement increases the effective length of the crank arm assembly to park the wiper arms below the normal wiping arc. A crank arm assembly according to this invention represents a novel alternative to the just described reverse-to-park crank arm assembly.